Hurricane Mk V prop

[Graham Boak]

The Mk.IID had the oval one, as standard for the Mk.II.  The Mk.IV had a more powerful engine, hence the more rectangular radiator - plus being armoured, of course.  As I understand it, the Merlins (27?) in the Mk.IV were almost as powerful, though this depends upon source, so would have to go digging in RR sources to find why the Mk.32 was preferred - I know it had the cropped impeller which gave a lower full throttle height and more power lower down which is why the FAA liked it.

[StevSmar]

15 hours ago, Graham Boak said:

The Mk.IID had the oval one, as standard for the Mk.II.  The Mk.IV had a more powerful engine, hence the more rectangular radiator - plus being armoured, of course.  As I understand it, the Merlins (27?) in the Mk.IV were almost as powerful, though this depends upon source, so would have to go digging in RR sources to find why the Mk.32 was preferred - I know it had the cropped impeller which gave a lower full throttle height and more power lower down which is why the FAA liked it.

Hi @Graham Boak, Did you mean the MkV had a more powerful engine?

 

My very very brief search on the power output of the MkIV’s engine vs the MkII’s suggested their engines were almost the same power, from which I concluded the only real difference was probably the height which the engine was tuned to provide maximum power at.

 

Is the consensus that the MkIV radiator, without armour, the same size as the MkII’s? This is my suspicion.

Edited November 6, 2018 by StevSmar
Poor grammar...

[Graham Boak]

I understood that the Mk.IV had some 1600hp, which considerably exceeds that of the Mk.II, but a quick look gave a lower value.  Hence my "depends upon source" comment above.  I have since looked in the RR Heritage Trust's The Merlin in Perspective.  This gives a value for the Merlin 27 of 1600hp at takeoff, 1635 at 2250ft and 1510hp at 9250ft, all at +18lb boost.  The Merlin 34 was a single stage engine with half an inch smaller supercharger diameter and 25lb lighter.  (The Mk.32 was the equivalent engine, but on the Barracuda.)  It was rated at 1640hp at takeoff and 1625hp at 3000ft, also at +18lb boost.  This suggests that there will have been little if any benefit from the Mk.V over the standard production Mk.IV, which perhaps explains its failure to impress.

 

It is possible that some benefit was expected at low level, but it doesn't seem to have been found.  Whether this was because the 35 wasn't as good as expected, or the 27 better, I can't say.  However I suspect the latter.  Possibly the 27 was a development not forseen at the time a decision was taken to experiment with the Mk.34.  However this would seem to imply at least the design-stage prospect of Mk.IVs with earlier XX-series engines, and these would have suffered from excess airframe weight.  (The Merlin Mk.27 is basically a Mk.24 which in turn is a Mk.22 stressed to +18lb boost.)

 

There may of course have been other behind-the-scenes decisions.  For example, was RR under pressure to produce enough Mk.22 variants for other types and looked to shift demand onto another line?  That's just a possible example, by the way, not a known problem.  (I do know that Coastal Command were demanding more Mk.22s for their Halifaxes, in view of unreliability experienced on their - possibly rather elderly - Mk.XXs.)

 

I'd rather sit on the fence at the moment regarding the late radiators.  I admit originally assuming that the Mk.IV simply had armour wrapped around the earlier design, but additional power requires additional cooling, and the Mk.IVs were largely intended for warmer climes anyway.  Going from the Merlin III to the XX required a deeper radiator, so the similar power jump  to the Mk.27 would seem to require a similar increase in size for the Hurricane Mk.IV's radiator.  Although from the looks of it there's no obvious reason for an even larger one on the Mk.V.